Depressurization systems in sands or other granular soils shall as a minimum and within the practical limits posed by the building, meet the following requirements.
Within the practical limits posed by the building, suction points shall be distributed as nearly equally as possible, and as follows:
- A maximum of 1,300 square feet (121 m2) per suction point, and
- Each required suction point shall be located not less than 6 feet (1829 mm) nor more than 18 feet (5486 mm) from the perimeter; and
- Multiple suction points shall be located within 36 feet (10 973 mm) of each other.
Suction pipe should be of a size appropriate to the air-flows of the system, a minimum of 1/2 inches (38 mm) in diameter at the fan, and shall not be reduced between the fan outlet and the final termination point.
Suction point pits excavated below the slab shall be sized to provide adequate pressure distribution beneath the slab. Dimensions of 22 inches (559 mm) in diameter and 11 inches (279 mm) deep, or excavation of 1 cubic foot (.02832 m3) of soil, shall be presumed to meet this requirement. Further the pit shall be filled with 1 inch (25 mm) size gravel.
Suction fans must be capable of developing minimum flows appropriate to the system at 1 inch water column pressure. Fans producing 100 cubic foot per minute (cfm) (.047 m3/s) at 1-inch water column pressure are presumed to meet this requirement.